1. Field of the Invention
The present invention relates, to a zoom lens with a vibration prevention (image stabilization) function suitable for silver photograph cameras, video cameras, digital cameras, electronic still cameras, and so on and, more particularly, is suitably applicable to a compact zoom lens of a high zoom ratio with relatively short back focus that realizes good correction for image vibration (image blur) during vibration (or inclination) of the zoom lens by moving a lens unit as part of the optical system or part of a lens unit so as to have a component normal to the optical axis, while achieving high optical performance.
2. Related Background Art
Various proposals have been made heretofore about optical systems in which the image blur was corrected by driving an optical element forming a photographing optical system (which will be called an optical vibration-preventing method).
In general, an important condition for such optical vibration-preventing methods is that the optical element of as small a weight as possible is driven by as small a drive amount as possible by a driving mechanism of relatively simple structure while the optical performance during prevention of vibration is maintained in a good level across as wide a range of vibration prevention angles as possible.
In the case of the zoom lenses of high zoom ratios actively developed recently, since a large amount of hand shaking is apt to occur, particularly, at the telephoto extreme, the vibration prevention function is considered to be important and a variety of proposals have been made about zoom lenses with a vibration prevention function designed to satisfy both the aforementioned condition and having a high zoom ratio.
Here the optical vibration-preventing methods include a shift vibration-preventing method of displacing (or shifting) a lens unit or part of a lens unit in the direction normal to the optical axis, a tilt vibration-preventing method of rotating a lens unit or part of a lens unit about a rotation axis normal to the optical axis, a variangle prism method of placing a member in which a relatively transparent liquid such as silicone oil or the like is interposed between transparent members, near or inside the photographing optical system and tilting the transparent member with respect to the optical axis to implement prevention of vibration by prism action, and so on, and there are various known examples of application thereof to the zoom lenses.
Particularly, the shift vibration-preventing method among such optical vibration-preventing methods is commonly adopted, because it has such advantages that the lens driving mechanism is relatively simple, that the degrees of freedom are greater in correction of chromatic aberration during prevention of vibration than in the case of the variangle vibration-preventing method, etc., and because relatively high optical performance is attained with a relatively simple structure, though the number of degrees of freedom are a little smaller in aberration correction than in the tilt vibration preventing method permitting selection of the rotation axis at a relatively free position.
The vibration-preventing zoom lenses employing the shift vibration-preventing method are suggested in Japanese Patent Applications Laid-Open No. 06-265827 (corresponding to U.S. Pat. No. 5,638,210), Laid-Open No. 07-318865, Laid-Open No. 08-82769, Laid-Open No. 01-189621 (corresponding to U.S. Pat. No. 5,270,857), Laid-Open No. 02-93620 (corresponding to U.S. Pat. No. 5,000,549), Laid-Open No. 03-179311 (corresponding to U.S. Pat. No. 5,168,403), and so on.
Japanese Patent Application Laid-Open No. 06-265827 discloses a zoom lens of such structure that the zoom lens consists of three lens units which are a first lens unit of positive refractive power, a second lens unit of positive refractive power, and a third lens unit of negative refractive power arranged in the order named from the object side, that zooming from the wide-angle extreme to the telephoto extreme is implemented so as to increase the spacing between the first lens unit and the second lens unit but decrease the spacing between the second lens unit and the third lens unit, that the second lens unit consists of a front subunit and a rear subunit, and that prevention of vibration is implemented by shifting the rear subunit in the direction normal to the optical axis.
Japanese Patent Application Laid-Open No. 07-318865 discloses a zoom lens which consists of a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, a fourth lens unit of positive refractive power, and a fifth lens unit of negative refractive power arranged in the order named from the object side and which has such structure that zooming from the wide-angle extreme to the telephoto extreme is effected so as to increase the spacing between the first lens unit and the second lens unit, decrease the spacing between the second lens unit and the third lens unit, increase the spacing between the third lens unit and the fourth lens unit, and decrease the spacing between the fourth lens unit and the fifth lens unit and so as to move at least the first lens unit and the fifth lens unit to the object side and that prevention of vibration is implemented by shifting the fourth lens unit in the direction normal to the optical axis.
Japanese Patent Application Laid-Open No. 08-82769 discloses a zoom lens which consists of a first lens unit of positive refractive power, a second lens unit of positive refractive power, a stop, and a third lens unit of negative refractive power arranged in the order named from the object side and which has such structure that zooming from the wide-angle extreme to the telephoto extreme is implemented so as to increase the spacing between the first lens unit and the second lens unit but decrease the spacing between the second lens unit and the third lens unit and that prevention of vibration is implemented by shifting the second lens unit in the direction normal to the optical axis.
Japanese Patent Applications Laid-Open No. 01-189621 and Laid-Open No. 03-179311 disclose two unit zoom lenses which consist of a first unit of positive refractive power and a second unit of negative refractive power, which is designed to perform zooming by moving the two lens units while changing the spacing between the two lens units, and in which prevention of vibration is implemented by shifting the first unit in the direction normal to the optical axis.
Japanese Patent Application Laid-Open No. 02-93620 discloses the zoom lens which is a two-unit zoom lens wherein the first unit consists of two lens subunits and wherein prevention of vibration is implemented by shifting one of the two lens subunits in the direction normal to the optical axis.
In the zoom lenses disclosed in Japanese Patent Applications Laid-Open No. 06-265827 and Laid-Open No. 08-82769, since the lens unit shifted for prevention of vibration (hereinafter referred to as a vibration-preventing lens unit) is composed of the large number of lens elements, the lens weight is relatively large and the load on driving of the lens is large during prevention of vibration.
In the zoom lens disclosed in Japanese Patent Application Laid-Open No. 07-318865, the lens structure of the vibration-preventing lens unit is relatively simple, but deterioration of aberration is encountered during prevention of vibration.
The zoom lenses disclosed in Japanese Patent Applications Laid-Open No. 01-189621, Laid-Open No. 03-179311, etc. have the problem that displacement amounts of the image during prevention of vibration by shifting the first unit are large as compared with shift amounts of the vibration-preventing lens unit (i.e., sensitivity is high) and it is thus difficult to control the shift system.
In the zoom lens disclosed in Japanese Patent Application Laid-Open No. 02-93620, it is difficult to simultaneously correct aberration variations due to zooming in the normal condition and aberration variations in the shift vibration prevention in application to lenses of high zoom ratios.
The specification of Laid-Open No. 02-93620 describes that the first unit is composed of three lens subunits and the shift vibration prevention may be carried out by shifting part of the lens subunits, but it fails to suggest any specific configuration of the lens structure etc. in that case.
An object of the present invention is to provide a never-before-known zoom lens of simple lens structure well-corrected for aberration both in the normal condition and in the vibration-preventing condition, while realizing a high zoom ratio.
For accomplishing the above object, a zoom lens according to one embodiment of the present invention is a zoom lens comprising the following lens units in the order named from the object side:
a first lens unit of a positive optical power, said first lens unit having a first lens subunit, a second lens subunit, and a third lens subunit arranged in the order named from the object side, the second lens subunit being moved so as to have a component normal to the optical axis, thereby displacing an image; and
a second lens unit of a negative optical power;
the zoom lens varying a spacing between the first lens unit and the second lens unit in order to implement zooming, and
wherein the following conditions are satisfied:
xe2x88x928.0 less than flb/ft less than xe2x88x920.5
xe2x88x929.0 less than fla/ft less than xe2x88x920.3
where ft is a focal length of the entire system at the telephoto extreme, flb a focal length of the second lens subunit, and fla a focal length of the first lens subunit.
Another zoom lens according to another embodiment of the present invention is a zoom lens comprising the following lens units in the order named from the object side:
a first lens unit of a positive optical power, the first lens unit having a first lens subunit, a second lens subunit, and a third lens subunit of a positive optical power arranged in the order named from the object side, the second lens subunit being moved so as to have a component normal to the optical axis, thereby displacing an image; and
a second lens unit of a negative optical power;
the zoom lens varying a spacing between the first lens unit and the second lens unit in order to implement zooming, and
wherein the first lens subunit has more lens elements than the third lens subunit.
Another zoom lens according to another embodiment of the present invention is a zoom lens comprising the following lens units in the order named from the object side:
a first lens unit of a positive optical power, the first lens unit having a first lens subunit, a second lens subunit of a positive optical power, and a third lens subunit of a positive optical power arranged in the order named from the object side, the second lens subunit being moved so as to have a component normal to the optical axis, thereby displacing an image; and
a second lens unit of a negative optical power;
the zoom lens varying a spacing between the first lens unit and said second lens unit in order to implement zooming, and
wherein a lens element adjacent on the object side to the second lens subunit has a positive optical power.
Another zoom lens according to another embodiment of the present invention is a zoom lens comprising the following lens units in the order named from the object side:
a first lens unit of a positive optical power, the first lens unit having a first lens subunit, a second lens subunit of a positive optical power, and a third lens subunit of a positive optical power arranged in the order named from the object side, the second lens subunit being moved so as to have a component normal to the optical axis, thereby displacing an image; and
a second lens unit of a negative optical power;
the zoom lens varying a spacing between the first lens unit and the second lens unit in order to implement zooming, and
wherein the first lens subunit has a plurality of lens elements of respective positive optical powers.
Another zoom lens according to another embodiment of the present invention is a zoom lens comprising the following lens units in the order named from the object side:
a first lens unit of a positive optical power, the first lens unit having a first lens subunit, a second lens subunit of a positive optical power, and a third lens subunit of a positive optical power arranged in the order named from the object side, the second lens subunit being moved so as to have a component normal to the optical axis, thereby displacing an image; and
a second lens unit of a negative optical power;
the zoom lens varying a spacing between the first lens unit and the second lens unit in order to implement zooming, and
wherein the third lens subunit consists of one lens element of a positive optical power.